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DEVD(8) FreeBSD System Manager's Manual DEVD(8)
NAMEdevd -- device state change daemon
SYNOPSISdevd [-dnq] [-ffile] [-lnum]
DESCRIPTION
The devd daemon provides a way to have userland programs run when certain
kernel events happen.
The following options are accepted.
-d Run in the foreground instead of becoming a daemon and log addi-
tional information for debugging.
-ffile Use configuration file file instead of the default
/etc/devd.conf. If option -f is specified more than once, the
last file specified is used.
-lnum Limit concurrent socket connections to num. The default connec-
tion limit is 10.
-n Do not process all pending events before becoming a daemon.
Instead, call daemon right away.
-q Quiet mode. Only log messages at priority LOG_WARNING or above.
IMPLEMENTATION NOTES
The devd utility is a system daemon that runs in the background all the
time. Whenever a device is added to or removed from the device tree,
devd will execute actions specified in devd.conf(5). For example, devd
might execute dhclient(8) when an Ethernet adapter is added to the sys-
tem, and kill the dhclient(8) instance when the same adapter is removed.
Another example would be for devd to use a table to locate and load via
kldload(8) the proper driver for an unrecognized device that is added to
the system.
The devd utility hooks into the devctl(4) device driver. This device
driver has hooks into the device configuration system. When nodes are
added or deleted from the tree, this device will deliver information
about the event to devd. Once devd has parsed the message, it will
search its action list for that kind of event and perform the action with
the highest matching value. For most mundane uses, the default handlers
are adequate. However, for more advanced users, the power is present to
tweak every aspect of what happens.
The devd utility reads /etc/devd.conf or the alternate configuration file
specified with a -f option and uses that file to drive the rest of the
process. While the format of this file is described in devd.conf(5),
some basics are covered here. In the options section, one can define
multiple directories to search for config files. All files in these
directories whose names match the pattern *.conf are parsed. These files
are intended to be installed by third party vendors that wish to hook
into the devd system without modifying the user's other config files.
Since devctl(4) allows only one active reader, devd multiplexes it, for-
warding all events to any number of connected clients. Clients connect
by opening the SOCK_SEQPACKET UNIX domain socket at
/var/run/devd.seqpacket.pipe.
FILES
/etc/devd.conf The default devd configuration file.
/var/run/devd.seqpacket.pipe The socket used by devd to communicate with
its clients.
/var/run/devd.pipe A deprecated socket retained for use with
old clients.
SEE ALSOdevctl(4), devd.conf(5)AUTHORS
M. Warner Losh
FreeBSD 10.2 August 14, 2014 FreeBSD 10.2